Common point of failure for this model, IIRC, is the mosfet or the terminals at the board dying. It's a 12v system so there's a few amps going through the wires.

If the bed thermistor shows a sensible value when it's at ambient temp (e.g., 20ºC), then it's probably ok. Move the bed around a bit and check whether it shows any fluctuating values. If that's ok, then follow the main heating wires back to the printer and see if you can find out where it's failed.